1. Field of the Invention
The present invention relates to a liquid crystal display device (LCD), and more particularly, to an array substrate for a transflective LCD and fabricating method thereof.
2. Discussion of the Related Art
Until recently, display devices generally have employed cathode-ray tubes (CRTs). Presently, many efforts are being made to study and develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panel (PDPs), field emission displays, and electro-luminescence displays (ELDs), as a substitute for CRTs. Of these flat panel displays, the LCD devices have several advantages such as high resolution images, lightweight, thin profile, compact size, and low voltage power supply requirements.
In general, an LCD device includes two substrates that are spaced apart and face each other, and a liquid crystal material layer interposed between the two substrates. The two substrates include electrodes that face each other, wherein a voltage supplied to each of the electrodes induces an electric field to the liquid crystal material layer. Accordingly, the alignment of liquid crystal molecules of the liquid crystal material layer changes in accordance with the intensity or direction of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the induced electric field.
Because the LCD device having a LCD panel is a non-luminous display device, the LCD device uses a light source such as a backlight unit which is disposed below the LCD panel. A light emitted from the backlight unit enters the LCD panel. The LCD using the backlight unit as a light source is a transmission type LCD. While the transmission type LCD has an advantage of displaying bright images even when the external environment is dark, the transmission type LCD consumes much power.
To improve the problem of high power consumption of the transmission type LCD, a reflection type LCD has been employed. The reflection type LCD uses an external light such as natural light. Because the reflection type LCD uses an external light, the reflection type LCD consumes less power than the transmission type LCD. A pixel electrode formed on an array substrate of the reflection type LCD is made of a reflective conductive material to reflect an external light, and a common electrode formed on a color filter substrate of the reflection type LCD is made of a transparent conductive material to transmit an external light. However, the reflection type LCD still has disadvantages in that an external light is required to display images and the brightness of the displayed images is low. Thus, a transflective LCD, which functions as either the transmission type LCD or the reflection type LCD depending on a light source, has been employed.
FIG. 1 is a plan view of a transflective LCD according to a related art.
In FIG. 1, a gate line 18 and a date line 35 are disposed on a substrate, crossing each other to define a pixel region P. The pixel region P includes a transparent region TA and a reflective region RA. A thin film transistor Tr is disposed near the crossing of the gate line 18 and the data line 35. The thin film transistor Tr includes a gate electrode 21, a source electrode 38, a drain electrode 41 and a semiconductor layer 9. The source electrode 38 is defined as a portion of the data line 35 overlapping the semiconductor layer 9. The source electrode 38 and the drain electrode 41 contact the semiconductor layer 9 through semiconductor contact holes 30a and 30b, respectively. A pixel electrode 65 contacts the thin film transistor Tr through a drain contact hole 47. A reflective electrode 62 is below the pixel electrode 65 and defines the reflective region RA. The pixel region P excluding the reflective electrode 62 is the transparent region TA. A storage line 24 is parallel to and apart from the gate line 18. Portions of the semiconductor layer 9 and the storage line 24, which overlap each other, act as first and second storage electrodes, and form a storage capacitor with a gate insulating layer. The portion of the semiconductor layer 9 overlapping the storage line 24 is an ohmic contact layer. An uneven pattern 59 is randomly formed in the reflective region RA.
FIG. 2 is a cross-sectional view taken along the line A—A in FIG. 1.
In FIG. 2, a semiconductor layer 9 including an active layer 9a, an ohmic contact layer 9b and a storage layer 9c is formed on a substrate 3, a gate insulating layer 15 is formed on the semiconductor layer 9, and a gate electrode 21 and a storage line 24 apart from the gate electrode 21 are formed on the gate insulating layer 15. A buffer layer 6 may be formed before forming the semiconductor layer 9. The storage layer 9b acts as a first storage electrode, the storage line 24 overlapping the storage layer 9b acts as a second storage electrode, and the gate insulating layer acts as a dielectric material for a storage capacitor StgC. Accordingly, the storage layer 9b, the storage line 24, and the gate insulating layer 15 define the storage capacitor StgC. On the gate electrode 21 and the storage line 24 is an interlayer 27. A source electrode 38 and a drain electrode 41 are formed on the interlayer 27 and contact the semiconductor layer 9 through semiconductor contact holes 30a and 30b, respectively.
A passivation layer 44 is formed on the source electrode 38, the drain electrode 41 and the interlayer 27 in a reflective region RA. In a transparent region TA, the passivation layer 44 is removed. The passivation layer 44 has a step between the transparent region TA and the reflective region RA. A surface of the passivation layer 44 has a uneven pattern 59. A reflective electrode 62 is formed on the passivation layer 44 in the reflective region RA, and the reflective electrode 62 has the uneven pattern 59 like the passivation layer 44. The passivation layer 44 and the reflective electrode 62 over the drain electrode 41 are patterned to form a drain contact hole 47 exposing the drain electrode 41. A pixel electrode 65 is formed on the reflective electrode 62 in the pixel region P. The pixel electrode 65 is made of a transparent conductive material and contacts the drain electrode 41 through the drain contact hole 47.
Because the transflective LCD according to the related art has the uneven pattern 59 formed randomly in the reflective region, an external light is reflected uniformly in all directions. Accordingly, the transflective LCD according to the related art reflects the external light efficiently. However, because the drain contact hole is formed in the reflective region, the area of the uneven pattern 59 in the reflective region is reduced. In addition, it is difficult to randomly form the uneven pattern in the reflective region.